The UP Postal Service Zip Codes are used to determine tariff charges on interstate moves. Since the early 2000’s, the process used to rate and estimate moves was converted from a paper process to a software-based computer process. The software uses the origin and destination zip codes to determine all of the variable factors to properly price the shipment. Most of the interstate rates have a cost-of-living (COL) component to them. Urban areas with a high COL have higher moving, insurance, and labor rates than rural, low COL areas. These COL factors are baked into the software using the zip codes so the rates can be micro-focused geographically rather than just using large county COL parameters. This gives our customers the best value proposition for our services.